/**
*      author: Y_Yao
*      created: 2025-01-18 20:33:44
**/

#include<bits/stdc++.h>

#define int LL
using namespace std;
using LL = long long;
const LL LLINF = 1e18;
const int INF = 0x3f3f3f3f;
int r;

void solve()
{
    cin >> r;
    int ans = 0;
    for(int i = 1;i < r;i++)
    {
        ans += floor(sqrt(r * r - (i + 0.5) * (i + 0.5)) - 0.5);
    }
    ans = ans * 4 + (r - 1) * 4 + 1;
    cout << ans << endl;
}

signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);

    int t = 1;
    //cin >> t;
    while(t--)
    {
        solve();
    }
    return 0;
}